Flexible pipe connected to an end fitting

ABSTRACT

The invention relates to a pipe structure ( 10 ) comprising a length of a flexible pipe connected to an end fitting, the flexible pipe comprising an armour layer ( 11; 19 ) and an underlying pipe layer ( 12; 11 ) to said armour layer, said underlying pipe layer having an outer surface around which armouring wires ( 111; 191 ) of an armouring layer are helically wound. The object of the present invention is to provide a coupling between a flexible pipe comprising armouring wires and an end fitting, the coupling exerting a relatively low bending or flexure strain on the wires during normal operation of the flexible pipe. The problem is solved in that the transition path of an armouring wire between the flexible pipe and the end fitting comprises an straight-line-section ( 194 ) between a wire-pipe-exit-point ( 195 ) where the wire extends away from its underlying pipe layer and a straight-line-end-point ( 196 ) on a support unit ( 15 ) of the end fitting where the armouring wire in question has its first tangential point of contact. This ahs the advantage that in a loaded situation where the armouring wires will elongate elastically leading to a change in the helical angle of the armouring wires, a pipe structure according to the invention will experience a slight twist and a controlled bending of the armouring wires on the surface of the support unit (due to a possible change in the base point of contact of the armouring wire with the support unit induced by the change of helical angle), thereby avoiding substantial bending of the individual armouring wires, which is of particular importance when the armouring wires are formed of a composite material. The invention may be used in flexible pipes for the off shore transport of fluids (e.g. oil).

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a flexible pipe for transporting afluid substance (e.g. oil or gas or a mixture thereof) and especially tothe connection of a flexible pipe to an end fitting for connecting theflexible pipe to an installation (at land or on a vessel at sea or onthe seabed) or for connecting to another pipe, e.g. another flexiblepipe or a rigid pipe. The invention deals with the subject of adapting arelatively flexible pipe to a relatively stiff end fitting. Theinvention relates specifically to a pipe structure comprising a lengthof a flexible pipe connected to an end fitting, the flexible pipecomprising an armour layer and an underlying pipe layer to said armourlayer, said underlying pipe layer having an outer surface around whicharmouring wires of an armouring layer are wound.

DESCRIPTION OF RELATED ART

Flexible pipes are used in a variety of applications, including watersupply lines, sewage lines for transporting chemicals such as liquidammonia and phosphoric acid in high-pressure off-shore applications inthe oil and gas industry.

The tensile armour layer or layers of the flexible pipe and the jointbetween this or these layers and the end fitting provides the majorityof the resistance to axial tensile loads acting on the assembly of theend fitting and the pipe. The joint between the flexible pipe and theend fitting performs the function of adapting a relatively flexible pipeto a relatively stiff fitting.

Un-bonded flexible pipes are conventionally reinforced with metallicwires, wound at an angle around the pipe to give the pipe its increasedflexibility. A conventional metallic armoured pipe is very stiff bothradially and axially, thus limiting the problem of the transition inflexibility of the structure from the running length of pipe to theconnector unit. Further, a conventional steel armouring element, wire,may yield to a local intensity of stress, caused by an abrupt change instiffness, without reducing the load bearing capacity of the element.Solutions for the anchoring of metallic armouring elements ofconventional un-bonded flexible pipes are available.

Conventional composite pipes are bonded and rigid, thus barrier- andreinforcing layers are fixed to each other at their interfaces. Further,the reinforcing fibres are embedded in resin, forming a continuouslayer. Rigid composite reinforced pipes are generally less stiff thantheir metallic counterparts and the anisotropy of the material—giving itdifferent properties in different directions—calls for a carefullyengineered transition to the connector unit. Many solutions can be foundfor the anchoring of the fibre reinforced layers in conventionalcomposite pipes, cf. e.g. U.S. Pat. Nos. 4,701,231 and 4,530,379.

Composite reinforced un-bonded flexible pipes differ from theconventional structures described above in that the pipe is axially andradially less stiff than the metallic reinforced flexible pipe and thelayers containing the composite reinforcement are not continuous, butconsist of a number of individual wires, each made of a compositematerial, which will not yield to a local stress intensity but ratherinitiate failure.

In the following, a novel solution to the efficient anchoring of a wirebased armouring in an end connector for a flexible pipe is presented.The solution may be used for pipes reinforced with metallic or compositearmouring wires and for bonded as well as un-bonded pipes.

SUMMARY

The object of the invention is to provide a coupling between a flexiblepipe comprising armouring wires and an end fitting, the couplingexerting a relatively low bending or flexure strain on the wires duringnormal operation of the flexible pipe (i.e. in a situation—within thedesign specifications of the pipe—of internal and/or external radialpressure and external tension in the longitudinal direction of thepipe).

The object of the invention is achieved by the invention described inthe accompanying claims and as described in the following.

A pipe structure according to the invention comprising a flexible pipeconnected to an end fitting is provided, the flexible pipe comprising anarmour layer and an underlying pipe layer to said armour layer, saidunderlying pipe layer having an outer surface around which armouringwires of an armouring layer are wound, the flexible pipe having alongitudinal axis wherein

said end fitting comprises

-   -   one or more anchoring elements adapted for anchoring at least        one of said armouring wires, and    -   a support unit arranged coaxially around said underlying pipe        layer    -   at least one of said armouring wires comprising        -   a conforming-wire-pipe-section forming a helical path and            conforming to the outer surface of said underlying pipe            layer of said flexible pipe at least over a part of its            length, and        -   a wire-end-fitting-section,        -   said two wire sections extending in opposite directions from            a wire-pipe-exit-point where said armouring wire separates            tangentially away from said underlying pipe layer, and    -   said wire follows an essentially straight line of a length        L_(free) between said wire-pipe-exit-point and a        straight-line-end-point on said support unit, said essentially        straight line part of the wire being defined as the        straight-line-section.

In the present context, the term ‘armouring wires’ is taken to meanelongate elements having e.g. a circular, rectangular (tape formed)cross sectional form or any other form appropriate for serving thepurpose of stabilizing the pipe in its longitudinal and/or radialdirection.

The ‘longitudinal axis’ of the flexible pipe is taken to mean the axisof symmetry in a direction of fluid flow defined by the flexible pipe inoperation when it is held in a straight line (uncurved) configuration.

A flexible pipe for transporting a fluid substance, egg. oil, has aninside which is in contact with the fluid substance during operation andan outside which is in contact with the environment, e.g. a marineenvironment. In the present context, the term ‘an outer surface’ of anelement in a flexible pipe is taken to mean a surface that faces towardsthe outside (as opposed towards the inside) of the flexible pipe (notnecessarily having a direct contact to the environment, though).Similarly, the terms a ‘convex’ or ‘an outward’ curvature and a‘concave’ or an ‘inward’ curvature, respectively, are taken to be seenrelative to the longitudinal axis of the flexible pipe.

In the present context, the term ‘an unloaded condition’ of a flexiblepipe or pipe structure is taken to mean a condition where the flexiblepipe is in a relaxed, unstressed situation, i.e. without beingpressurised from inside or outside and without being subject to externaltwist or longitudinal stress.

In the present context, the terms ‘wire-pipe-exit-point’ and ‘astraight-line-end-point’ are taken to mean the end points of contactbetween an armouring wire and, respectively, the underlying pipe layerand the support unit of the end fitting, between which the armouringwire follows an essentially straight line. Instead of points of contact‘wire-pipe-exit-point’ and ‘a straight-line-end-point’ are to beinterpreted as lines or curves of contact, if said wire has a crosssection that adapts to the surface of said underlying pipe layer and/orsaid support unit, e.g. a tape form. The same applies to a‘support-unit-exit-point’ (see later) where the armouring wire leavesthe surface of the support unit for being locked in one of the anchoringelements.

In a preferred embodiment the ratio of the ‘free length’ or‘straight-line-section’ L_(free) (in an unloaded condition of the pipe)of an armouring wire to its maximum cross sectional dimension D_(wire)is larger than 2, preferably in a range from 2-20, more preferred in arange from 5-10, the ‘free length’ being defined as the length of anarmouring wire between its exit point from the underlying pipe layer(the ‘wire-pipe-exit-point’) and its point of contact with the supportunit of the end fitting (‘straight-line-end-point’).

An advantage of the invention is that in a loaded situation comprising acombination of internal pressure and external tension and where thearmouring wires will elongate elastically leading to a change in thehelical angle of the armouring wires, a pipe structure according to theinvention will experience a slight twist and a controlled bending of thearmouring wires on the surface of the support unit (due to a possiblechange in the base point of contact of the armouring wire with thesupport unit induced by the change of helical angle), thereby avoidingsubstantial bending of the individual armouring wires. This is forexample of particular importance when the armouring wires are formed ofa composite material. A complete and simple anchoring can then beincorporated in the end fitting design at any point after the‘straight-line-end-point’ on the support unit (in the direction of theend fitting, i.e. when viewed from the pipe towards the end fitting), asthe wire after this point is only stressed in its own direction.

The various parts of an end fitting may preferably be made of structuralmaterials e.g. metals such as steel, titanium, aluminium, reinforcedpolymers such as fibre glass/polyester, carbon-fibre/epoxy, etc. Theparts may e.g. be manufactured by a numerically controlled machine or bymoulding.

In an embodiment of the invention, the wire-end-fitting-section isarranged to follow a predefined termination path between saidwire-pipe-exit-point and one of said anchoring elements when said pipestructure is in an unloaded condition. The dynamic range of locations ofthe wire-pipe-exit-point and the straight-line-end-point may bepredetermined according to the normal operating conditions of the pipestructure. The part of the wire-end-fitting-section of the armouringwire that is located after the dynamic range of locations of thestraight-line-end-point (when viewed in a direction of the end fitting)may be fixed to a predetermined path on the support unit (e.g. usingguiding channels or the like) to simplify the mounting of the flexiblepipe to the end fitting.

In an embodiment of the invention, the straight-line-section isessentially unsupported between said wire-pipe-exit-point and saidstraight-line-end-point on said support unit. The term ‘essentiallyunsupported’ is in the present context taken to mean having a negligibleeffect on the deformation behaviour of the wire.

In an embodiment of the invention, the straight-line-section extendsaway from said longitudinal axis when viewed from saidwire-pipe-exit-point.

In an embodiment of the invention, the straight-line-section of saidarmouring wire has a tangential point of contact with said support unitin said straight-line-end-point. In this embodiment, the armouring wirehas a free (i.e. mechanically unrestricted) linear path between thepoints of contact with the underlying pipe layer and the support unit.Alternatively, the armouring wire may be strained in contact with (butwithout locking it to) the support unit e.g. by a surrounding body (e.g.in the form of an assisting element, see later), in which case the slopeof the straight-line-section of the armouring wire may deviate from thetangent to the support unit at the point of contact.

The underlying surface to the armour may have significant stiffnessestablished through an insert. This will reduce the angular change ofthe helix of the armouring wires during loading.

In an embodiment of the invention, said underlying pipe layer of saidflexible pipe comprises an armouring reinforcement on a section of thepipe structure including said wire-pipe-exit-point and extending in adirection of the end fitting as defined by a direction from the flexiblepipe towards the end fitting.

An armouring reinforcement may be present (if necessary for theoperating conditions of the pipe in question) and comprise an annualarmouring body forming part of the underlying pipe layer and is intendedfor supporting the flexible pipe over the part of the end fitting wheresome of the armouring wires are leaving the flexible pipe for beingsupported by the support unit, thereby weakening the armouring effect.Alternatively an armouring reinforcement may form part of the supportunit and annularly enclose the underlying pipe layer so that thewire-pipe-exit-point is located on the armouring reinforcement-part ofthe support unit. In an alternative embodiment, this substitutearmouring layer may be inserted on the inner side of the armouring layeror layers in question, in which case the wire-pipe-exit-point will belocated on the so-called underlying pipe layer. The purpose of thearmouring reinforcement is to give a mainly radial stiffness over itslength and represents a transition between the flexible pipe and thestiff end fitting.

In an embodiment of the invention, said predefined termination pathfurther comprises a supported-wire-section running on the outer surfaceof said support unit from said straight-line-end-point to asupport-unit-exit-point where the armouring wire leaves the surface ofsaid support unit for being locked in one of said anchoring elements,said supported-wire-section essentially constituting a geodetic curvebetween said straight-line-end-point and said support-unit-exit-point onsaid outer surface of said support unit.

In the present context the term ‘a geodetic curve’ is taken to mean acurve on a surface for which the curve has a primary normal vector whichin all points is identical to the normal vector of the surface. Ageodetic curve on a surface represents the shortest distance along thesurface between two points on the surface. A geodetic curve on a surfacehas a geodetic curvature ρ_(g)=0, the geodetic curvature of a curve at apoint P on a surface being defined as the length of the projection(calculated with sign) of the vector of curvature on the tangent planeof the surface at the point P. The vector of curvature ρn of curve r(s)at a point P (given as r₁(s)) is defined as d²r₁/ds²=ρn, ρ being thecurvature of the curve at the point P and n a unit vector.

The term ‘essentially constitutes a geodetic curve’ is in the presentcontext taken to mean that the path in question follows a geodetic curveon the surface of the support unit in question within the mechanicalprocessing tolerances, e.g. so that the relative length differencebetween the actual path and the geodetic curve is less than 5%,preferably less than 1%.

The advantage hereof is that the armouring wires are located in stablepositions when the flexible pipe is in an unloaded state because allwires are positioned to follow a shortest possible path on the supportunit of the end fitting. This minimizes the ‘repositioning’ of thearmouring wires when the flexible pipe is loaded.

A geodetic curve between two points on a surface may in practice befound by means of a string with no bending resistance, which undertension will find the shortest path between to points.

In an embodiment of the invention, said support unit has an outersurface that describes a surface of revolution with an axis ofrevolution that coincides with the longitudinal axis of the flexiblepipe. This has the advantage of providing a symmetric element which isrelatively easily manufactured. Alternatively, the support unit may takemany other forms, e.g. more complex forms where elements are arranged toreceive individual armouring wires. In an embodiment of the invention,the supporting surface of the support unit in the area where thestraight-line-end-point is located is individually formed for differentwires having their straight-line-end-point located on the support unit.An advantage of hereof is that assembly of the wires to the end fittingis eased and reliability improved. In an embodiment of the invention,the supporting surface of a wire is a single curved surface orientedsuch that every normal to this surface lies in a plane that is parallelto any plane containing the longitudinal axis of the pipe. In thepresent context, “a single curved surface” is taken to mean a surfacethat curves in only one dimension (a simple example is a cylindergenerated by a circle, but any other curve may be used). The use of asingle curved surface in the present construction has the advantage thatthe construction of the individual surface parts are well-suited forimplementation with standard manufacturing tools (e.g. numericallycontrolled tools).

Typically, the support unit is arranged around and ‘resting on’ theunderlying pipe layer. It might, however, alternatively be arrangedaround the underlying pipe layer without touching it or resting thereon.In an embodiment of the invention, the support unit comprises an annularbody with an opening that fully encloses the armouring layer in questionaround which the support unit is mounted coaxially, the opening being ofa form and size that allows the support unit to be positioned relativeto the underlying pipe layer in such a way that a straight line path(‘the straight-line-section) is defined between a wire-pipe-exit-pointon the underlying pipe layer to a point of contact (‘thestraight-line-end-point’) on the inner outline of said opening of thesupport unit. In an embodiment of the invention, the surface around thelocation of the predicted points of contact during normal operation isformed so that its surface is concave when seen relative to thelongitudinal axis of the flexible pipe in a cross section including saidaxis. In an embodiment of the invention, the support unit is arrangedannularly around the underlying pipe layer, e.g. in the form of anannular ring (e.g. a torus) with an inner diameter that is larger thanthe diameter of the underlying pipe layer so that an armouring wire mayhave its straight-line-end-point on the annular ring surface and asupported-wire-section that extends through the inner opening of theannular ring for being locked in an anchoring element.

In an embodiment of the invention, the anchoring elements form part ofthe support unit.

In an embodiment of the invention, said support unit has an outersurface which includes a part of a torus on which the‘straight-line-end-point’ is located.

The term ‘an outer surface which includes a part of a torus’ is in thepresent context taken to mean that said surface has a part that has theshape of a part a torus, e.g. corresponding to a 15 or 45 or 90 degreecut of a fully revolved torus (the quoted angles being centre angles ofthe local circle that generates the torus by a 360° rotation about itsaxis of revolution).

In a preferred embodiment, the pipe structure is adapted so that theSAME geodetic 5 curve is used by an armouring wire when the flexiblepipe is in an unloaded situation as when the flexible pipe is loaded,the only difference being that the point of contact changes along thelength of the geodetic curve in question (whereby the angle of the freepath of the armouring wire varies). The decisive parameters determiningthe course of the armouring wire on the torus surface are, respectively,a) the diameter of the layer on which the armouring is wound (e.g. theunderlying pipe layer), b) the helix angle (the winding angle e.g.relative to the longitudinal axis of the flexible pipe, e.g. 54°), c)the diameter of the circle of the torus body in a cross sectionperpendicular to a direction of revolution (the local diameter), and d)the diameter of the circle of revolution generating the torus (theglobal diameter).

In practice it may be necessary to deviate from this optimum geometryfor other considerations, but with the knowledge acquired through thissolution, the additional stresses may be predicted and an acceptablecompromise can be achieved.

In an embodiment of the invention, said support unit has a convex partwith an outer surface with an outward curvature and said‘straight-line-end-point’ is located on said convex part of the supportunit.

This has the advantage of providing a relatively easily manufacturablepart that may be positioned annularly around and resting on saidunderlying pipe layer and with an outer surface that extends away fromthe longitudinal axis at least over the convex (e.g. torus-formed) partof the surface of the support unit where the armouring wire in question‘lands’ (.i.e. around the predicted location of thestraight-line-end-point when the flexible pipe is operated within itsspecifications).

In an embodiment of the invention, said support unit comprises at leasta first and a second body, the outer surfaces of each body having adifferent geometrical form, and said straight-line-end-point is locatedon said first body. In an embodiment of the invention, the outersurfaces of said first and second bodies of the support unit areseparated by a gap. In an embodiment of the invention, said first andsecond bodies of the support unit are adjoined. In an embodiment of theinvention, said second body of the support unit comprises dedicatedelements for receiving and/or guiding one or more armouring wires.

In an embodiment of the invention, said support unit comprises at leasta first and a second body, said first body of the support unit has anouter surface which includes a part of a torus, and said second body hasan outer surface that describes a surface of revolution, both surfaceshaving the same axis of revolution, said axis coinciding with thelongitudinal axis of the flexible pipe, and both surfaces havingcoinciding tangents in a joining point in a cross sectional planeincluding the axis of revolution.

In a preferred embodiment, said second body is a cylinder. Alternativelythe second body may include a conoidous part, whose surface extends awayfrom or verge on its axis of revolution when viewed from the torusformed part of the support unit in the direction of the end fitting. Inanother preferred embodiment, the support unit comprises a concave partextending from the convex part of the support unit hosting thestraight-line-end-point in a direction towards the wire-pipe-exit-point,the concave part having an outer surface with an inward curvature (or alinear surface, when viewed in a cross section including thelongitudinal axis of the flexible pipe).

In an embodiment of the invention, said second body comprises guidingelements for guiding armouring wires received from said first body.

In a preferred embodiment the second body comprises guiding channels forguiding armouring wires received from the first body. The purpose of theguiding channels is to lead the armouring wires from the first body inthe direction of the anchoring elements. The channels may extend fullyor partially over the length of the second part of the support unit. Thechannels may be fully or partially embedded in the support unit, i.e.may constitute buried channels over a part of their longitudinalextension. The inclusion of guiding channels is an advantage for themounting of the end fitting with the flexible pipe and feasible becausethe armouring wire will only be stressed in its own longitudinaldirection after leaving the first body of the support unit.

In an embodiment of the invention, said anchoring elements for lockingsaid armouring wires to said end-fitting are distributed on one or moreterminating parts.

It may be an advantage to separate the anchoring elements from thesupport unit by providing the anchoring elements in one or moreterminating parts, to be able to customize the support unit and theterminating part(s) individually.

In an embodiment of the invention, the flexible pipe comprises more thanone armouring layer and separate support units and terminating parts areallocated to each layer.

In an embodiment of the invention, separate support units andterminating parts are arranged sequentially after each other along thelongitudinal axis of the flexible pipe, e.g. first the support unit(s)and terminating part(s) corresponding to the outermost armouring layerfollowed by the support unit(s) and terminating part(s) corresponding tothe second outermost armouring layer, etc.

In another embodiment of the invention, corresponding of said separatesupport units and terminating parts, respectively, are arrangedconcentrically around each other, the element corresponding to theinnermost armouring layer being arranged closest to the axis of theflexible pipe (i.e. support units are arranged concentrically aroundeach other followed in a longitudinal direction by terminating partsbeing arranged concentrically around each other).

In yet another embodiment of the invention, a combination ofsequentially and concentrically arranged support units and terminatingparts are used.

In an embodiment of the invention, the straight-line-section of anarmouring wire is surrounded by a material which does not substantiallyalter the deformation behaviour of the flexible pipe and the wire.

To avoid the intrusion of impurities, it may be advantageous to fill thespace around the free path part (or straight-line-section) of thearmouring wire path with a filler that does not substantially effect thefree movement of the armouring wire. Such material could e.g. be asuspension or emulsion of a polymer, e.g. polyethylene or polyurethane.A further advantage hereof is that such a material may be used forcooling or flushing purposes, if the end fitting is cooled with acoolant, e.g. water to remove heat from the transported fluid of theflexible pipe, e.g. an oil of an elevated temperature compared to roomtemperature.

In an embodiment of the invention, said pipe structure further comprisesan assisting element arranged coaxially around said armour layer andadapted for maintaining at least one of said armouring wires in contactwith the outer surface of said underlying pipe layer, and said armouringwire conforms to said underlying pipe layer between said assistingelement and said wire-pipe-exit-point in which the armouring wireseparates tangentially away from said underlying pipe layer.

In an embodiment of the invention, the pipe structure comprises anassisting element arranged coaxially around said underlying pipe layerand adapted for guiding at least one of said armouring wires.

In an embodiment of the invention, an assisting element is adapted forsupporting armouring wires from a particular one of the one or morearmouring layers of the flexible pipe.

In an embodiment of the invention, an annular assisting element isarranged around an armouring layer to maintain at least one armouringwire in contact with the support unit at the straight-line-end-point, inwhich case the slope of the straight-line-section of the armouring wiremay differ from the tangent to the surface of the support unit in thestraight-line-end-point.

In an embodiment of the invention, an assisting element forms part ofthe end fitting.

In another embodiment of the invention, an assisting element forms partof the flexible pipe, e.g. in the form of an armour holding layer aroundan armouring layer, the armour holding layer being terminated at a pointof the flexible pipe structure located before the support unit of theend fitting, when viewed in a direction of the end fitting.Alternatively, an assisting element may take the form of a discreteannular ring positioned around an armouring layer at certain intervalsover a length of the flexible pipe, one of these rings being used forguiding an armouring wire towards its corresponding support unit.

In an embodiment of the invention, the flexible pipe is an un-bondedflexible pipe, preferably comprising a tube formed by an inner armouringlayer (carcass) surrounded by a liquid tight inner liner and one, two ormore outer armouring layers.

An un-bonded flexible pipe has the advantage over a corresponding bondedtype that it is more flexible.

In an embodiment of the invention, said flexible pipe comprises twolayers of helically wound armouring wires, the winding angles withrespect to the longitudinal direction of the flexible pipe being between50 and 60°, such as between 53 and 56°, e.g. 55° said armour layerspreferably comprising helically wound wires which are wound in oppositedirections in neighbouring layers. This has the advantage of providing abalanced pipe whose length has a relatively small dependence on itsoperating conditions such as pressure and temperature.

For a composite reinforced un-bonded flexible pipe, no solutions areavailable to facilitate the transition in stiffness of the pipe andconnector structure without drastically reducing the load bearingcapacity of the composite armour. This is a result of the opposingdesires to control the stiffness on one hand and make a complete,secure, and thus very stiff anchoring on the other hand.

In an embodiment of the invention, said armouring wire or wires are madeof a composite material, said composite material preferably comprise oneor more polymers, such as epoxy, thermoplastic and polyurethane,optionally comprising reinforcing fillers such as fibres and/orwhiskers. An advantage thereof is that the pipe is stronger (tensilestrength) and lighter (which is a special advantage during layout anduse in deep see environments), more corrosion resistant in certain mediathan a corresponding pipe comprising metallic armouring wires.

A composite material is in the present context taken to mean a materialcomprising several parts, e.g. of different atomic structure, differentchemical composition, e.g. a matrix of a given material comprisingenclosed elements of another material or micro-structural constitution(e.g. micro-crystalline grains in an otherwise amorphous matrix) or alayered material comprising distinct layers of different materials oridentical materials in a sandwich structure.

In an embodiment of the invention, said armouring wire or wires are inthe form of a layered wire comprising 2 or more layers of materialswhich may be identical or different from each other. A layered wire is awire made up of thin strips, assembled longitudinally on each other.This has the advantage of being able to combine properties of differentmaterials, the tapes/strips may be pre-fabricated, provide ease ofhandling, and/or be readily deformable in the pipe manufacturingprocess.

In an embodiment of the invention, said armour layers of the wire orwires are made from one or more of the materials selected from the groupconsisting of metals, such as steel, thermoplastic polymers such aspolyurethane and thermosetting polymers such as epoxy, said polymericmaterials optionally comprise reinforcing fillers such as fibres and/orwhiskers.

In an embodiment of the invention, said armouring wire or wires is/arein the form of a layered wire comprising 2 or more layers of materialswhich layers being held together by a wrapping material and/or byadhesive forces. An advantage of using a wrapping material is that itmay save the use of adhesives. An advantage of using an adhesive is thatit maintains positions of the layers and the assembly structure inproduction and provides means/possibility to splice.

In an embodiment of the invention, the or each armour layer comprisesone or two armouring wires. In another embodiment of the invention, eacharmouring layer comprises a multitude of armouring wires.

In an embodiment of the invention, said armouring wire(s) is/are flat,said wire or wires having a square formed cross section, optionally asquare formed shape with rounded corners. This has the advantage ofproviding a compact solution that minimizes the volume around the wirestaken up by air (when compared e.g. to a solution with circular wires).

In an embodiment of the invention, each of the layers of the flexiblepipe is fixed to the end-fitting.

In an embodiment of the invention, said end-fitting comprises an axiallyextending through opening, said armouring wire or wires being supportedby the outer surface of said support unit, wherein the outer surfacemeans the surface turning away from the axially extending throughopening.

In an embodiment of the invention, the armouring wire or wires is/areanchored by being embedded in a casting material, preferably in the formof a polymer such as an epoxy or a cementidious material. The term ‘acementidious material’ is in the present context taken to mean amaterial bound together by cement (which is a product comprising amongother things calcium, carbon, silicon, characterized in that it cures toa hard, stony compound in a reaction with water). Cementidious materialsmay be concrete, mortar, Portland White™, all characterised by a binder(cement) and a filler, usually rocks, stones, sand, etc. (i.e. silicabased particles). This has the advantage of providing means foranchoring, by adhesion, mechanical locking, etc.

In an embodiment of the invention, the end-fitting comprises one or morelocking cavities said armouring wire or wires is/are anchored in saidlocking cavity or cavities.

In an embodiment of the invention, the armouring wire or wires beinganchored by use of a spreader element driven into the wire or wires insaid locking cavity or cavities.

In an embodiment of the invention, at least one locking cavity has alength dimension defined as the length dimension of a wire mounted inthe locking cavity. The cross sectional area perpendicular to the lengthof the locking cavity differs along its length in one or more steps orcontinuously, wherein a first cross section area perpendicular to thelength of the locking cavity is smaller, such as at least 5% smaller,such as at least 30% smaller than a second cross section areaperpendicular to the length of the locking cavity, wherein the firstcross section is closer to the support unit than the second crosssection.

In an embodiment of the invention, the armouring wire or wires is/areanchored by use of a spreader element driven into the wire or wires inthe part of said locking cavity or cavities where a first crosssectional area perpendicular to the length of the respective lockingcavity is larger than a second cross sectional area perpendicular to thelength of the respective locking cavity, the second cross section beingtaken closer to the support unit than the first.

In an embodiment of the invention, the armouring wire or wires is/areanchored to the end-fitting by use of a spreader element driven into thewire to thereby spread the wire into two or more laminates whereby thelaminated wire or wires is fixed against the wall or walls of a lockingcavity formed in the end-fitting. In a preferred embodiment, thearmouring wire or wires is/are embedded in a casting material in thelocking cavity, preferably additionally using a wedge element driveninto the wire.

In an embodiment of the invention, the flexible pipe comprises twoarmour layers and the end fitting comprise two annular support units,the wire or wires of a first armour layer being supported by a firstannular support unit, and the wire or wires of a second armour layerbeing supported by a second annular support unit.

In an embodiment of the invention, the pipe structure comprises areinforcement sleeve layer placed below the one or more armouring layeror layers, said reinforcement sleeve layer extend along the pipestructure in a length which include the section of the pipe structurebetween the wire-pipe-exit-point and the straight-line-end-point, saidreinforcement sleeve preferably extend along the pipe structure in alength which includes the anchoring point or points on the end-fitting.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps or components but does not preclude thepresence or addition of one or more other stated features, integers,steps, components or groups thereof

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained more fully below in connection with apreferred embodiment and with reference to the drawings in which:

FIG. 1 shows a pipe structure according to the invention comprising asimplified flexible pipe connected to an end fitting,

FIG. 2 shows a path of an armouring wire from the underlying pipe layerof the flexible pipe to the support unit of the end fitting,

FIGS. 3.a and 3.b show different perspectives of a pipe structureaccording to the invention with two armouring layers with oppositewinding angles,

FIGS. 4.a, 4.b, 4.c show an embodiment of an anchoring element forlocking an armouring wire to an end fitting by means of a spreaderelement, the locking cavity having a stepwise changing cross sectionalarea,

FIG. 5.a, 5.b, 5.c show an embodiment of an anchoring element forlocking an armouring wire to an end fitting by means of a spreaderelement, the locking cavity having a continuously changing crosssectional area,

FIG. 6 shows an example of a flexible pipe suitable for being connectedto an end fitting in a pipe structure according to the invention, and

FIG. 7 shows partial view of an embodiment of a pipe structure accordingto the invention, FIG. 7.a being a side view, FIG. 7.b a cross sectionalview and FIG. 7.c a perspective view.

The figures are schematic and simplified for clarity, and they just showdetails which are essential to the understanding of the invention, whileother details are left out.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a pipe structure according to the invention wherein an openend of a flexible pipe is connected to an end fitting, the flexible pipecomprising armouring wires that are locked to the end fitting inanchoring elements thereby fixing the flexible pipe to the end fitting.

The pipe structure 10 (comprising a flexible pipe and an end fitting)comprises two armouring layers, a lower armouring layer 11 and an upperarmouring layer 19, each comprising a helically wound armouring wire(111 and 191, respectively). For clarity, only one armouring wire ofeach layer is shown in the drawing. It should be noted that thearmouring wires 111 and 191 may represent examples of a multitude ofarmouring wires constituting the lower and upper armouring layer,respectively. It should further be noted that the parts 193, 113 (seelater) of the armouring wires of the upper and lower armouring layer,respectively, may not originate from (be part of) the same physical wireas is indicated by the reference numerals 191, 111, respectively. Thearmouring wires of the two armouring layers are wound with oppositewinding angles (as seen relatively to the longitudinal direction 121 ofthe flexible pipe). The winding angles {acute over (α)}_(upper), {acuteover (α)}_(lower) of the upper and lower armouring layer, respectively,are preferably in the range between 50 and 60°, e.g. {acute over(α)}_(upper)=−{acute over (α)}_(lower)=55°.

The lower armouring layer 11 surrounds an underlying pipe layer 12 inthe form of a cylindrical liner (optionally surrounding an innercarcass, not shown in FIG. 1 but shown as 2 in FIG. 6) around which thearmouring wire 111 is helically wound. The upper armouring layer 19surrounds the lower armouring layer 11 (which thus represents ‘theunderlying pipe layer’ for the upper armouring layer) around which thearmouring wire 191 is helically wound. An intermediate layer (not shown)between the two armouring layers 11, 19 may be inserted (in which casethe intermediate layer represents the underlying pipe layer for theupper armouring layer). The armouring wires 1 1, 191 of the lower andupper armouring layers have a tape formed cross section when viewedperpendicular to a longitudinal direction of a wire (i.e. the wire iswider in a dimension that is tangential to the underlying pipe layerthan in a dimension perpendicular to that). An advantage of the tapeform, is that it conforms to the curvature of the underlying pipe layerand that it is relatively easy to avoid the introduction of twist to thewire during assembly.

The underlying pipe layer 12 for the lower armouring layer 11 comprisesan armouring reinforcement section 122 that is designed to compensatethe decreasing armouring effect of the armouring wires in the endfitting part of the pipe structure. The armouring reinforcement section122 comprises a cylindrical part 124 extending through the end fittingto the terminating flange 181 (for connecting the pipe structure toinstallations or to another pipe at land or at sea) and a conical part123 which adapts the dimension of the cylindrical part 124 to that ofthe underlying pipe layer 12 (or alternatively to that of the underlyingpipe layer of the upper armouring layer), thereby providing a smoothtransition section for the armouring wires 111, 191 of the lower andupper armouring layers 11, 19. In an embodiment of the invention, thecylindrical part 124 is terminated in the first support unit 15 (i.e.does not extend through the end fitting in its fall length to theterminating flange). In an embodiment of the invention, the lowerarmouring layer 11 runs beneath armouring reinforcement section 122 tobe terminated in the support unit 17 and/or terminating part 16. Inanother embodiment of the invention, the cylindrical part 124 isterminated in the “second” support unit 17 (i.e. does not extend throughthe end fitting in its full length to the terminating flange). In anembodiment of the invention, the lower armouring layer 11 runs beneaththe support unit 15 to be terminated in the support unit 17 and/orterminating part 16.

The armouring wire 191 of the upper armouring layer 19 has aconforming-wire-pipe-section 192 which conforms to the underlying pipelayer 11 (including a part of the armouring reinforcement section 122)until a wire-pipe-exit-point 195 where the armouring wire tangentiallyextends away from the underlying pipe layer 11 (in the form of thearmouring reinforcement section 122). The part of the armouring wire 191from the wire-pipe-exit-point to its termination in an anchoring element141 in a terminating part 14 is termed ‘the wire end fitting section’193. The terminating part 14 may preferably be an integral part of thesupport unit 15 or alternatively be an independent part adjoined thesupport unit. Extending from the wire-pipe-exit-point 195 the armouringwire has an unsupported ‘free path’ or straight-line-section 194 that isterminated by the tangential point of contact 196 (‘thestraight-line-end-point’) with the support unit 15. The support unitwhich is adapted to receive the armouring wire after its separation fromthe underlying pipe layer has a rotational symmetry around thelongitudinal axis 121 of the flexible pipe and is arranged to surroundthe underlying pipe layer (i.e. including the armour reinforcement 122).The outer surface of the ‘landing part’ 152 of the support unit 15 onwhich the straight-line-end-point is located during normal operatingconditions of the flexible pipe takes the form of a part of a torus (theouter surface 152 may alternatively be any convex surface of revolutionrelative to the longitudinal axis of the flexible pipe). The adaptingpart 151 of the support unit 15 serves as an intermediate body betweenthe cylindrical part 124 of the armouring reinforcement section 122 andthe landing part 152 of the support unit 15. The outer surface of theadapting part 151 has an inward curvature relative to the longitudinaldirection of the flexible pipe. It might, however, take on other formse.g. conical or even have an outward curvature, e.g. continue the torusform of the landing part 152.

The armouring wire 191 is supported by the support unit 15 from thestraight-line-end-point 196 to an exit point 197 where the wire isreceived and fixed by an anchoring element 141. Embodiments of theanchoring element are discussed in relation to FIGS. 4 and 5. Guidingchannels 153 are arranged on or in connection with the transition part154 of the support unit that supports the armouring wire between thelanding part 152 and the terminating part 14 which hosts the anchoringelements 141. The anchoring of the wire may alternatively be located onthe transition part 154. The transition part of the support unit has aconical outer surface that verge on the longitudinal axis 121 of theflexible pipe when viewed in a direction of the terminating flange 181.This yields a preferred, relatively compact solution. It mayalternatively extend outwards, and possibly have an outward curvature.It is preferred that the wire end fitting section 193 of the path of thearmouring wire is adapted to be free from ‘points of discontinuity’,i.e. that the outer surface transitions between the various parts of thesupport unit 15 are ‘smooth’.

FIG. 1 further shows a support unit 17 and terminating part 16 for thelower armouring layer 11. The upper armouring layer 19 is arranged onthe lower armouring layer 11 and the lower layer comprises a tape formedwire 111. The wire 111 of the lower layer is for descriptive purposesdivided in a conforming-wire-pipe-section 112 and an end fitting section113. The armouring layer 11 extends beneath the support unit 15 andterminating part 14 for the upper armouring layer 19. The armouring wire111 of the lower armouring layer 11 is terminated on the support unit 17and/or the terminating part 16.

In FIG. 2, the path of an armouring wire at the transition between theflexible pipe and the end fitting is shown. In a preferred embodiment asillustrated in FIG. 1, each armouring layer has its own support unit (15and 17 in FIG. 1). FIG. 2 and the following description may apply to thelower armouring layer 11 as well as to the upper armouring layer 19 ofFIG. 1. The armouring wire 211—preferably of a compositenature—initially conforming to the underlying surface 22 at a prescribedhelical angle with the longitudinal axis 221 of the flexible pipe, isformed away from the underlying pipe surface 22, in such a way that thetangent direction at the point of separation 215 from the underlyingsurface is followed by the wire until this direction becomes tangentwith the outer surface of a torus 252 at a straight-line-end-point 216,this torus being a part of the support unit 25. In a preferredembodiment, the wire 211 then follows a geodetic curve from the point oftangency 216 on the torus, until another surface 254 supports the wire.The geodetic curve is found by winding under tension. On this secondsurface the wire again follows a geodetic curve and may be securely andcompletely anchored by various means in an anchoring element (not shown,but corresponding to 141 in FIG. 1). Between the pipe tangent point 215(the wire-pipe-exit-point) and the torus tangent point 216 (thestraight-line-end-point), the wire follows a straight line path 214. Thewire, having a rectangular cross section, is twisted to conform to bothsurfaces at the tangent points. In a preferred embodiment of theinvention, the wire is surrounded by a soft filler material (e.g. anemulsion of a polymer) at least over the free path, unsupported sectionbetween the tangent points. The soft material is chosen to have anegligible effect on the deformation behaviour of the pipe and compositewire. This soft material may provide cooling or flushing of theenvironment surrounding the composite wire. The filler may be introducedin the volume of the end fitting limited by the support unit and theunderlying pipe layer (e.g. the reinforcement section) and an outerlayer surrounding the armouring layers or by the casing 18 of the endfitting (cf. FIG. 1) extended in the opposite direction of the endfitting.

FIGS. 3.a and 3.b show an embodiment of a part of a pipe structureaccording to the invention. The figures show the part of the pipe-to-endfitting transition, where the armouring wires of an armouring layerextend away from their underlying pipe layer for being received by asupport unit of an end fitting. FIGS. 3.a and 3.b show the same sectionof the pipe structure exhibiting the same features but from differentperspectives. A cut-out is made, so that the central opening of the pipestructure in the longitudinal direction 321 of the flexible pipe isexposed. An armouring reinforcement section 322 comprising a cylindricalsection 324 and a conical section 323 surrounds an underlying pipe layer32. Two armouring layers 31 and 39 each comprising helically wound,tape-formed armouring wires are shown. The lower armouring layer 31 iswound on the underlying pipe layer 32 and on the armouring reinforcementsection 322 which it leaves for landing on a lower support unit 35, eacharmouring wire of the lower armouring layer 31 having an unsupportedsection between the armouring reinforcement section 322 and the lowersupport unit 35. The upper armouring layer 39 is wound on the lowerarmouring layer 31 which it leaves for landing on an upper support unit37, each armouring wire having an unsupported section there between. Thelower and upper support units 35, 37 supporting the lower and upperarmouring layers 31, 39, respectively, are arranged concentricallyaround the underlying pipe layer 32 (with the armouring reinforcementsection 322) and the upper support unit 37 is arranged around the lowersupport unit 35.

The layers 301 and 302 indicate other pipe layers, e.g. inner armouringlayers, cf. e.g. FIG. 6 where various layers of an exemplary flexiblepipe are shown. The support units 35, 37 and the anchoring elements (notshown) for fixing the armouring wires to the end fitting are surroundedby an outer casing 38.

FIG. 4.a shows an anchoring element 42 for locking an armouring wire 41to an end fitting by means of a wedge formed spreader element 44 havinga narrow end 441 and a broad end 442, the locking cavity 45 for holdingthe wire end and the spreader element having a stepwise changing crosssectional area, so that a first cross sectional area A1 is larger than asecond cross sectional area A2, both taken perpendicular to thelongitudinal direction of the wire in the locking cavity, the firstcross section 421 (corresponding to A1) being taken closer to the broadend 442 of the spreader element 44 than the second cross section 422(corresponding to A2) when the spreader element 44 is placed in thelocking cavity 45, and at least one stepwise change 423 of the crosssection of the locking cavity is present between the first and secondcross sections 421 and 422. The anchoring element 42 for fixing anarmouring wire 41 to an end fitting comprises a locking cavity 45 formedin a solid material (which may be part of a terminating element hostinga number of anchoring elements, cf. 14 or 16 in FIG. 1) and awedge-formed element 44 adapted to be driven into the end of anarmouring wire 41 thereby separating the wire in two parts 411, 412 overa certain length (when viewed in a cross section including alongitudinal axis of the wire) and fixing the wire to the solid materialof the walls of the locking cavity 45. An adhesive 432 may optionally beintroduced between the wedge and the split parts of the wire(represented by 411 and 412 in the cross sectional view of FIG. 4.a). Anadhesive 431 may preferably be introduced between the wire 41 and thewalls of the locking cavity 45. The wedge 44 may preferably be made ofsimilar materials as the wire 41, e.g. composite, metallic (e.g. steel,aluminium, titanium), or another composite (than the wire). The wire maypreferably be made of a composite material or a metallic material in anycombination. The adhesive may e.g. comprise epoxy, polyurethane, athermoplastic adhesive, a cementidious material, all possibly comprisingparticles/fibres/whiskers.

FIG. 4.b shows a cross sectional view of the armouring wire 41 in thelocking cavity 45 in the cross section indicated by 421 in FIG. 4.awhereas FIG. 4.c shows a cross sectional view of the armouring wire 41in the locking cavity 45 in the cross section indicated by 422 in FIG.4.a. In FIG. 4.b the cross sectional area Al comprises the wedge 44 andthe two separated parts 411, 412 of the wire embedded in an adhesive 431fully of partially filling the empty volume between the wire and thesurrounding solid material of the anchoring element 42. In FIG. 4.c thecross sectional area A₂ comprises essentially only the wire 41surrounded by the solid material of the anchoring element 42.

Various methods of securing an armouring wire to an end termination aredisclosed in our co-pending international patent application entitled “Amethod of securing reinforcement wires to an end termination of apipeline or a cable, an end termination, and uses of the method and theend termination” published as WO-A-01/07818 and which is incorporatedherein by reference.

FIG. 5.a shows an anchoring element 52 for locking an armouring wire 51to an end fitting by means of a wedge formed spreader element 54 havinga narrow end 541 and a broad end 542, the locking cavity 55 for holdingthe wire end and the spreader element having a continuously changingcross sectional area (at least over a part of its length along thewire), so that a first cross sectional area A₁ is larger than a secondcross sectional area A₂, both taken perpendicular to the longitudinaldirection of the wire in the locking cavity, the first cross section 521(corresponding to A₁) being taken closer to the broad end 542 of thespreader element 54 than the second cross section 522 (corresponding toA₂) when the spreader element 54 is placed in the locking cavity 55. Theanchoring element 52 for fixing an armouring wire 51 to an end fittingcomprises a locking cavity 55 formed in a solid material (which may bepart of a terminating element hosting a number of anchoring elements,cf. 14 or 16 in FIG. 1) and a wedge-formed element 54 adapted to bedriven into the end of an armouring wire 51 thereby separating the wirein two parts 511, 512 over a certain length (when viewed in a crosssection including a longitudinal axis of the wire) and fixing the wireto the solid material A moulding 53 may preferably be introduced betweenthe wire 51 and the walls of the locking cavity 55.

FIG. 5.b shows a cross sectional view of the armouring wire 51 in thelocking cavity 55 in the cross section indicated by 521 in FIG. 5.awhereas FIG. 5.c shows a cross sectional view of the armouring wire 51in the locking cavity 55 in the cross section indicated by 522 in FIG.5.a. In FIG. 5.b the cross sectional area A1 comprises the laminatedwire 51, which comprises alternating layers 513, 514 of a wire material(e.g. composite material, metallic tape, or other) and an adhesivematerial, respectively, the laminated wire being embedded in a ‘grout’or moulding 53 (e.g. a particle filled casting material, cementidiousmaterial, a polymer, epoxy) which again is surrounded by the solidmaterial of the anchoring element 52. In FIG. 5.c the cross sectionalarea A₂ comprises essentially only the armouring wire 51 (with layers513, 514) surrounded by the solid material of the anchoring element 52.

A possible way of constructing laminated armouring wires is e.g.disclosed in our co-pending international patent application no.PCT/DK02/00355 entitled “A method of manufacturing a reinforcementelement for a flexible pipe” which is incorporated herein by reference.

FIG. 6 shows an ordinary structure of a flexible reinforced pipe 1 withits different layers. The flexible pipe in FIG. 6 consists of an innerliner 3 surrounding a carcass which is formed by a helically wound metaltape 2 that forms an inner pipe. The metal tape 2 is formed with flapsin the manufacture which engage each other so as to lock the individualturns of the metal tape 2 to each other in such a manner that thecarcass can be bent in its longitudinal direction. Since the innercarcass per se is not tight, the surrounding inner liner 3 serves thepurpose of preventing flow of fluids to or from the interior of thepipe.

One or more layers of profiles 5, 6 are helically wound externally onthe inner liner 3, said profiles forming turns of a great angle (e.g.80-90°) relative to the longitudinal direction of the pipe. Because ofthe great angle, the profiles will primarily be capable of absorbingradial forces that occur because of internal or external pressures. Theinternal pressures occur in the operation of the pipe. The externalpressures are caused partly by the hydrostatic pressure of thesurroundings and partly by mechanical impacts during the laying of thepipe.

The turns thus form a compressive reinforcement which prevents’ theinner liner 3 from bursting because of a high pressure on the inner sideof the pipeline, or from collapsing because of a high pressure on theouter side of the pipeline.

It is additionally shown in FIG. 6 that the compressive reinforcementhas externally applied thereto a tensile reinforcement, which consistsof one or more layers 7, 8 comprising helically wound armouring wires.

An intermediate jacket may be interposed between the compressivereinforcement and the tensile reinforcement, serving the purpose ofpreventing fluids from migrating between the compressive reinforcementand the tensile reinforcement.

These layers may finally be surrounded by an outer sheath 9.

The tensile reinforcement 7, 8 is usually composed of two helicallywound layers of steel profiles with opposite winding direction. Thearmouring wires may alternatively be made of other materials, e.g.composite materials.

In conventional pipe systems, the tensile reinforcement is secured tothe end termination by welding. It may, however, as discussed above withrelation to FIGS. 4 and 5 preferably be secured by means of a spreaderelement driven into the end of an armouring wire, the wire end with thespreader element being secured in a wedge-formed cavity a method (cf.also WO-A-01/07818).

FIG. 7 shows an embodiment of a pipe structure according to theinvention. FIG. 7.a shows a side view of the pipe structure, FIG. 7.b aview along a longitudinal axis of the pipe structure, and FIG. 7.c aperspective view. An armour wire with a wedged end and two principal endfitting components, the support unit and an armouring reinforcementsection unit, are shown.

For illustrative purposes only one wire of one layer is shown in FIG. 7.Other wires of the armouring layer 7 of which the wire 71 forms part maybe locked in the ‘empty’ anchoring elements (here termination slots 73)of the support unit 72. It is understood that these components are apart of an assembly and as such do not show the complete end fitting.Wires of possible other layers may likewise be terminated in the lockinggrooves or alternatively in a separate set of grooves (as conceptionallyillustrated in FIGS. 1 and 3).

The FIGS. 7.a to 7.c show a wire 71 representing the armour layer 7which is to be terminated in part by the components shown and in part byadditional components that make up the complete end fitting structure,comprising a conforming-wire-pipe-section 711 resting by surface contacton the armouring reinforcement section 74 that is designed to compensatethe decreasing armouring effect of the armouring wires in the endfitting part of the pipe structure. The armouring reinforcement sectionis placed under the armour layer 7 and comprises a cylindrical section741 shown here and other sections not shown that facilitate a transitionto the underlying layer (cf. e.g. FIG. 1).

In an embodiment of the invention, the support unit 72 containsindividual wire-support-and termination-slots 73 for receiving andterminating each wire 71. In an embodiment of the invention, each slotis made in the plane of tangency 75 (FIG. 7.b) of the wire to beterminated by that particular slot. This ensures that pipe deformationand resulting change of armouring wire angle with respect to thelongitudinal axis 77 of the pipe is transformed into pure bending aboutthe thinnest dimension of the armouring wire, thereby minimisingstresses. Each supporting surface 731 of the support unit 72 is a singlecurved surface (i.e. a surface that curves in only one dimension),oriented perpendicular to the tangent plane 75 wherein the correspondingarmouring wire has its wire-pipe-exit-point, straight-line-section andstraight-line-end-point. Therefore, the change in angle of the armourlayer associated with applying tension and pressure to the pipe occursin this tangent plane, moving the straight-line-end-point on the samecurve on the supporting surface, namely the curve created by theintersection of the single curved supporting surface and the tangentplane.

In the embodiment of the invention shown in FIG. 7, the anchoringelements (here termination-slots 73) form part of the support unit 72.The anchoring elements are created by the individual-wire-support-andtermination-slots 73 which create locking cavities 735 by the surfaces733 and 734. The locking cavities 735 provided by the support unit arefurther enclosed by components not shown, such as an end flange to thesupport unit 72 and outer casing, represented schematically on FIG. 7.bby the circle 76.

The armouring wire 71 of the armour layer 7 has aconforming-wire-pipe-section 711 which conforms to the underlying pipelayer that includes the armouring reinforcement section 74 until awire-pipe-exit-point 712 where the armouring wire tangentially extendsaway from the underlying pipe layer and thereby the armouringreinforcement section 74. The wire extends over a straight-line-section713 to the tangential point of contact 714 (thestraight-line-end-point), where a curved surface 731 of theindividual-wire-support-slot 73 provides a smooth and controlledtransition to the wire anchoring. The straight wire section 715 of thetransition to the anchoring section 735 ensures that the anchoring isloaded only by a pure unidirectional tension, which maximise theeffectiveness of the anchoring principle. The wire is lead into thelocking cavity 735 by the straight-slot-section 732, wherein the wire isanchored. The anchoring is provided by driving a wedge formed spreaderelement 718 into the end of the wire 71, and secure the split armourwire parts 716 and 717 to the spreader element by gluing. Furthermore,anchoring is provided by the principle described in FIG. 5, since theangled surfaces 733 and the locking-cavity-side 734 provides anexpanding cross sectional area of the locking cavity 735, and the wedgedend 719 of the wire 71 also provides an increasing cross section, bothin the direction towards the broad end of the wedged wire. An angledsurface 733 and its adjacent straight-slot section surface 732 maypreferably form an angle between 25° and 50°. A locking-cavity-sidesurface 734 and its adjacent straight-slot section surface 732 maypreferably form an angle between 0° and 30°. The offset of the wedgedwire end 719 relative to the locking cavity 735, in the direction of andaway from the straight-slot-section 732, creates room for a mouldingmaterial, as described with respect to FIG. 5.

In an embodiment of the invention the angled surfaces 733 andlocking-cavity-side 734 and even the surface of thestraight-slot-section 732 may be a continuous surface, providing asmooth transition from the straight-slot-section 732, conforming to thewire thickness dimension and to the expanding cross sections in thelocking cavity 735.

It is clear that the FIG. 7.a-7 c shows only the principle forterminating a single wire layer, however it can applied to two or morelayers in the manner given by FIG. 1 or FIG. 3.

An advantage of the embodiment of FIG. 7 is that because every wire isoriented on its own individually part-support-surface 731, assembly ofthe wires to the end fitting is eased because the anchoring elements aresecurely separated and shaped to ensure that wires do not slip on thesurface and are not located in a wrong position thereby improvingreliability. Further each anchoring element has its own separate cavityfor fastening a wire with a corresponding wedge.

Some preferred embodiments have been shown in the foregoing, but itshould be stressed that the invention is not limited to these, but maybe embodied in other ways within the subject-matter defined in thefollowing claims.

1. A pipe structure comprising a flexible pipe connected to an endfitting, the flexible pipe comprising an armour layer and an underlyingpipe layer to said armour layer, said underlying pipe layer having anouter surface around which armouring wires of an armouring layer arewound, the flexible pipe having a longitudinal axis wherein said endfitting comprises one or more anchoring elements adapted for anchoringat least one of said armouring wires, and a support unit arrangedcoaxially around said underlying pipe layer at least one of saidarmouring wires comprising a conforming-wire-pipe-section forming ahelical path and conforming to the outer surface of said underlying pipelayer of said flexible pipe at least over a part of its length, and awire-end-fitting-section, said two wire sections extending in oppositedirections from a wire-pipe-exit-point where said armouring wireseparates tangentially away from said underlying pipe layer, and saidwire follows an essentially straight line of a length L_(free) betweensaid wire-pipe-exit-point and a straight-line-end-point on said supportunit, said essentially straight line part of the wire being defined asthe straight-line-section.
 2. A pipe structure according to claim 1wherein said wire-end-fitting-section is arranged to follow a predefinedtermination path between said wire-pipe-exit-point and one of saidanchoring elements when said pipe structure is in an unloaded condition.3. A pipe structure according to claim 1 wherein saidstraight-line-section is essentially unsupported between saidwire-pipe-exit-point and said straight-line-end-point on said supportunit.
 4. A pipe structure according to claim 1, wherein saidstraight-line-section extends away from said longitudinal axis whenviewed from said wire-pipe-exit-point.
 5. A pipe structure according toclaim 1, wherein said straight-line-section of said armouring wire has atangential point of contact with said support unit in saidstraight-line-end-point.
 6. A pipe structure according to claim 1,wherein said underlying pipe layer of said flexible pipe comprises anarmouring reinforcement on a section of the pipe structure includingsaid wire-pipe-exit-point and extending in a direction of the endfitting as defined by a direction from the flexible pipe towards the endfitting.
 7. A pipe structure according to claim 2, wherein saidpredefined termination path further comprises a supported-wire-sectionrunning on the outer surface of said support unit from saidstraight-line-end-point to a support-unit-exit-point where the armouringwire leaves the surface of said support unit for being locked in one ofsaid anchoring elements, said supported-wire-section essentiallyconstituting a geodetic curve between said straight-line-end-point andsaid support-unit-exit-point on said outer surface of said support unit.8. A pipe structure according to claim 1, wherein the support unitcomprises elements arranged to receive individual armouring wires.
 9. Apipe structure according to claim 8 wherein the supporting surface ofsaid support unit where said straight-line-end-point is located isindividually formed for different wires having theirstraight-line-end-point located on said support unit.
 10. A pipestructure according to claim 9 wherein the supporting surface of a wireis a single curved surface oriented normal to the pipe tangent plane ofthe wire, containing the said straight-line-section of said wire.
 11. Apipe structure according to claim 1, wherein said support unit has anouter surface that describes a surface of revolution with an axis ofrevolution that coincides with the longitudinal axis of the flexiblepipe.
 12. A pipe structure according to claim 1, wherein said supportunit has an outer surface which includes a part of a torus on which thestraight-line-end-point is located.
 13. A pipe structure according toclaim 1, wherein said support unit has a convex part with an outersurface with an outward curvature and said straight-line-end-point islocated on said convex part of the support unit.
 14. A pipe structureaccording to claim 1, wherein said support unit comprises at least afirst and a second body, said first body of the support unit has anouter surface which includes a part of a torus, and said second body hasan outer surface that describes a surface of revolution, both surfaceshaving the same axis of revolution, said axis coinciding with thelongitudinal axis of the flexible pipe, and both surfaces havingcoinciding tangents in a joining point in a cross sectional planeincluding the axis of revolution.
 15. A pipe structure according toclaim 14 wherein said second body comprises guiding elements for guidingarmouring wires received from said first body.
 16. A pipe structureaccording to claim 1, wherein said anchoring elements for locking saidarmouring wires to said end-fitting are distributed on one or moreterminating parts.
 17. A pipe structure according to claim 16 whereinthe flexible pipe comprises more than one armouring layer and separatesupport units and terminating parts are allocated to each layer.
 18. Apipe structure according to claim 1, wherein said straight-line-sectionof an armouring wire is surrounded by a material which does notsubstantially alter the deformation behaviour of the flexible pipe andthe wire.
 19. A pipe structure according to claim 1, wherein theflexible pipe is an un-bonded flexible pipe, preferably comprising atube formed liquid tight inner liner and one or more armour layers,preferably two or more armour layers.
 20. A pipe structure according toclaim 1, wherein said flexible pipe comprises two layers of helicallywound armouring wires, the winding angles with respect to thelongitudinal direction of the flexible pipe being between 50 and 60degrees, such as between 53 and 56 degrees, said armour layerspreferably comprising helically wound wires which are wound in oppositedirections.
 21. A pipe structure according to claim 1, wherein saidarmouring wire or wires are made of a composite material, said compositematerial preferably comprise one or more polymers, such as epoxy,thermoplastic and polyurethane, optionally comprising reinforcingfillers such as fibres and/or whiskers.
 22. A pipe structure accordingto claim 1, wherein said armouring wire or wires are in the form of alayered wire comprising [[2]] two or more layers of materials which maybe identical or different from each other.
 23. A pipe structureaccording to claim 22 wherein said armour layers of the wire or wiresare made from one or more of the materials selected from the groupconsisting of metals, such as steel, thermoplastic polymers such aspolyurethane and thermosetting polymers such as epoxy, said polymericmaterials optionally comprise reinforcing fillers such as fibres and/orwhiskers.
 24. A pipe structure according to claim 1, wherein saidarmouring wire or wires is/are in the form of a layered wire comprisingtwo or more layers of materials which layers being held together by awrapping material and/or by adhesive forces.
 25. A pipe structureaccording to claim 1, wherein the or each armour layer comprises one ortwo or a multitude of armouring wires.
 26. A pipe structure according toclaim 1, wherein said armouring wire(s) is/are flat, said wire or wireshaving a square formed cross section, optionally a square formed shapewith rounded corners.
 27. A pipe structure according to claim 1, whereineach of the layers of the flexible pipe are fixed to said end-fitting.28. A pipe structure according to claim 1, wherein said end-fittingcomprises an axially extending through opening, said armouring wire orwires being supported by the outer surface of said support unit, whereinthe outer surface means the surface turning away from the axiallyextending through opening.
 29. A pipe structure according to claim 1,wherein the armouring wire or wires is/are anchored by being embedded ina casting material, preferably in the form of a polymer such as an epoxyor a cementidious material.
 30. A pipe structure according to claim 1,wherein the end-fitting comprises one or more locking cavities, saidarmouring wire or wires is/are anchored in said locking cavity orcavities.
 31. A pipe structure according to claim 30 wherein thearmouring wire or wires being anchored by use of a spreader elementdriven into the wire or wires in said locking cavity or cavities.
 32. Apipe structure according to claim 30 wherein at least one locking cavityhas a length dimension defined as the length dimension of a wire mountedin the locking cavity, and the cross sectional area perpendicular to thelength of the locking cavity differs along its length in one or moresteps or continuously, wherein a first cross sectional areaperpendicular to the length of the locking cavity is smaller, such as atleast 5% smaller, such as at least 30 % smaller than a second crosssectional area perpendicular to the length of the locking cavity,wherein the first cross section is closer to the support unit than thesecond cross section.
 33. A pipe structure according to claim 32 whereinthe armouring wire or wires is/are anchored by use of a spreader elementdriven into the wire or wires in the part of said locking cavity orcavities where a first cross sectional area perpendicular to the lengthof the respective locking cavity is larger than a second cross sectionalarea perpendicular to the length of the respective locking cavity, thesecond cross section being taken closer to the support unit than thefirst.
 34. A pipe structure according to claim 1, wherein the armouringwire or wires is/are anchored to the end-fitting by use of a spreaderelement driven into the wire to thereby spread the wire into two or morelaminates whereby the laminated wire or wires is fixed against the wallor walls of a locking cavity formed in the end-fitting.
 35. A pipestructure according to claim 1, wherein the flexible pipe comprises twoarmour layers and the end fitting comprise two annular support units,the wire or wires of a first armour layer being supported by a firstannular support unit, and the wire or wires of a second armour layerbeing supported by a second annular support unit.
 36. A pipe structureaccording to claim 1, wherein the pipe structure comprises areinforcement sleeve layer placed below the one or more armouring layeror layers, said reinforcement sleeve layer extends along the pipestructure in a length which include the section of the pipe structurebetween the wire-pipe-exit-point and the straight-line-end-point, andsaid reinforcement sleeve preferably extend along the pipe structure ina length which include the anchoring point or points on the end-fitting.